CHEVROLET SILVERADO DEALER PROBLEM

1978 Chevrolet Silverado • 99,000 miles

1978 chevy 4x4 has new speedometer head and cable. Old speedo was broken do replaced it. Now at 20 mph on speedo it is runnning about 40 mph with follow up car at 30 35 it is running about 50 60 it is a steel gear with 20 teeth tires are 33x12.50R15 LT has a 3 '' body lift?

You need a gear with a lot more teeth so it turns slower. 32 to 34 teeth is common. Your local dealer may still have some, otherwise you'll have to search the salvage yards. The gear housing must be turned to the appropriate orientation depending on the diameter of the new gear.